Highly polymeric polymethylene terephthalates



United States Patent Ofiice 3,055,868 HIGHLY POLYMERIC POLYMETHYLENE TEREPHTHALATE James Eric McIntyre and John Skinner Macuab Robertson, Han-agate, England, assiguors to Imperial Chemi- 3,055,868 Patented Sept. 25, 1962 have now found that magnesium compounds suitable as ester-interchange catalysts can be inactivated without formation of an insoluble precipitate, by the addition of at least a stoichiometric equivalent of antimony trifluoride and that the polycondensation of the ester-intercal Industries Limited, London, England, a corporation 5 change product then gives a clear and colourless polyof Great Britain ester. Although this inactivation can be undertaken N a u Filed l f 317,090 using other trihalides of antimony, for example the tri- Clmms pnonty applicatlon Great Bmam June 1958 chloride or the tribromide, the colour of polymer pre- 7 Clalms' 260-75) 10 pared using these compounds is inferior to that obtained This invention relates to the manufacture of highly W en s g ntimony trifluo-ride. olymeric polymethylene hm l more i According to the present invention we provide a process larly to the use of a catalyst system in the manufacture f r he man fa ture of fibre and film-forming highly of these polyesters, polymeric polymethylene terephthalates by reacting a di- In the common method of commercial manufacture alkyl tefephthalaie With glycol of The Series of highly polymeric polymethylene terephthalates, a di- H0(CH2)nOH alkyl terephthalate is ester-interchanged in the presence of an ester-interchange catalyst andthe resulting product, W lnclllslve an polycondenslng the resulta bis-hydroxyalkyl terephthalate, is polycondensed in the F 5 bls'hydrexyeilkyl. terep1 1tha1ate!. Wherem the esterpresence of a y polycondensation catalyst Commonly interchange reaction 15 carried out in the presence of at the polycondensation catalyst is added to the initial este-rleast one eatalytlc mag neslun 1 compqllnd and e P 3- interchange reaction mixture f majority f prior condensation reaction 1s carried out 1n the presence of art potllycondensatiorlr catalysts do not normally interfere 2:15:3 aggfng lg fig l gflgg gl g lgsz g g egfivgifi with t e ester-interc an e reaction.

It is known, for eximple, from British Patent No. amount to magnesium P P 804,753 to use antimony fluoride as a catalyst in the poly W have found that the glyeelexlde, acetate, carbonate, condensation ofabis-hydroxyalkyl terephthalate, obtained OXPde and p i e 0f magneslum are particularly by an ester-interchange process, using manganese formate sultfable as ig l l f l i of these We as a catalyst, to a highly polymeric polymethylene ter- P use e g 0X1 e e f ephthalate, buth it is stated therein that this caitalyst mus-t is a ti c l gl e fize f gggi tgyi tg ghigfifig ggg be added to t e reaction mixture imme iate rior to the polycondensa-tion stage, as it strongly in higits the ethylene glycol the s ing materials, other alkyl estepinterchange tage esters of terephthahc acid such as diethyl terephthalate Many ester-interchange catalysts if allowed to remain or Such as 114 butenedlel may also be in active form during the polycondensation stage tend gl gs-alg gz l lgid gfh liz gi ellgg i i g imgl i r is? ;sifri? or g iiiidz oi lflgf g gi g i zi fig allsgl esters of other acids such as those of isophthalic have in the ast been preferred for use as ester-intereel change cataly sts, but such compounds suffer from the Although 1t 13 to ee understood that W not hmlt commercial disadvantage that they produce insoluble pre- 40 Purselves to the 'eddltlen P the megneslum compound cipitates in the final polyester which give undesirable P We eXemPhfY, We Prefer add amounts effects in fibres, films and the like produced from these 0f mm compound between 0.01 and 0.15 mole polyesters. i percent, based on the dialkyl terephthalate used.

It is known, for example, from British latent 610,137 The followmg exemplesr In which all Parts P and U.S.P. 2,543,028 to use magnesium compounds such eentagee e e r ln-ustrate but not llmlt the as the oxide or formate, as ester-interchange catalysts scope of P I in the manufacture of highly polymeric polymethylene e followmg ester mterchange 9 f gi e terephthalates. Such magnesium compounds give a rapid ieactlogs g ig l LEE g 1 reaction rate and a colourless ester-interchange product. ifiz g ii 97 s hi y g g g It allowed to remain in an active form in the polycon- 50 a chrgnd intopa flask g g with theyestepgiriep densation Stage they are superior compounds of calchange catalyst and heated until the theoretical amount cium in that no insoluble precipitate is formed. Howof methanol had been evolved The terdnterchange ever, they do promote colour formation in the final product was charged (together with the polycondensa polyester and this disadvantage has hitherto restricted 55 tion catalyst if not already present) to a polymerisation their commercial use as catalysts. We have found that t be, free glycol was distilled off, and the residue was y adding a Strong acid this Colour fermation can be polymerised at a pressure of (LOGS-0.02 mm. with a greatly reduced or prevented, but We a also found slow bleed of nitrogen through the molten mass for a that the majority of strong acids give rise to magnesium period of two hours. The intrinsic viscosity thus attained salts which are insoluble in the resulting polyester. We is a measure of the rate of polycondensation.

Table I Polycondensation catalyst or colour inhibitor Exlalrnple Ester interchangveetiagltltlyst, percent by Time of addition Melt colour Percent by Weight relialigtfignegsger i111 i tii) carbonate (basm) 0'03! Antilmony trioxide 0.04% .l Before and alter .gjsdoggifggggiYI:

3 ia 'r'oiiifi fiifiiidfiietiu'fijjjl ran .Y: "3 4 do Antimony trifiuoride 0.05% d0 Clear, colourless 0.7

Ester interchange and polymerisation reactions were carried out under the conditions used for Examples 1-4, using the magnesium compounds listed in Table II as ester interchange catalyst and in each case adding antimony trifluoride (0.05% by weight on dimethyl terephthalate charged) at a temperature of 160l90 C. alter the esterinterchange was complete.

Table II Optical density at 400;: of soln. in dichloroacetic acid Ester interchange catalyst, crcent by Ex. No. weight on dimcthyl terep ithalate The optical density at 400; of a 10% solution of the polymer in dichloroacetic acid is a more accurate measure of the yellowness of the polymer than visual comparison. All the polymers made with antimony trifluoride above had solution densities of 0.1 or below and appeared colour-less, but slightly grey in bulk. Polymers made according to Examples 1 and 2 had solution optical densities of 0.25 and 0.38 respectively and were pale yellow in appearance. Polymers made using the ester-interchange catalysts of Examples 6 to 9 together with antimony trioxide as polymerisation catalyst were also pale pellow in appearance.

By comparison polymer was made by the method of Example 4, but using antimony trichloride (0.062% by weight on dimethyl terephthal-ate charged) instead of antimony trifluoride. The solution optical density of the resulting polymer was 0.15, which represented a substantial improvement over the use of antimony trioxide.

When this example was repeated in a stainless steel polymerisation vessel, although little or no corrosion of the stainless steel was detected, the iron content or the polymer was 20-40 ppm. higher than with antimony trioxide or antimony trifiuoride. Antimony trifiuoride did not affect the iron content and is therefore preferable to antimony trichlor-ide.

Polymer made by the method of Example 4 but using antimony tribromide (0.1% by weight on dimethyl terephthalate charged) was pale red-brown in colour, and inferior to the product made using antimony trifluoride.

In each example, the polyester formed was capable of being converted into fibres, filaments and films by a melt extrusion process.

What we claim is:

1. In the process of manufiacture of fiberand filmforming highly polymeric polymethylene terephthalates wherein a dialkyl terephthlate is reacted under ester interchange conditions with a glycol of the series HO (CH OH where n- 2-l0 inclusive, and the resulting glycol terephthalates are polycondensed in the presence of a polycondensation catalyst system to form the highly polymeric polymethylene terephthalate; the improvement which comprises (1) employing as the sole ester-interchange catalyst between about 0.01 and about 0.15 mole percent of said dialkyl terephthalate of a catalytic magnesium compound and (2) carrying out the polycondensation reaction in the presence of said magnesium compound to which has been added a polycondensation catalyst consisting essentially of antimony trifluoride in at least an equivalent amount to the magnesium compound present.

2. A process according to claim 1 wherein the highly polymeric polymethylene terephthalate is polyethylene terephthalate.

3. A process according to claim 1, wherein the magnesium compound used is the glycoloxide.

4. A process according to claim 1, wherein the magnesium compound used is the carbonate. 5. A process according to claim 1, wherein the magnesium compound used is the oxide.

6. A process according to claim 1, wherein the magnesium compound is the acetate.

7. A process according to claim 1, wherein the magnesium compound used is the terephthalate.

References Cited in the file of this patent UNITED STATES PATENTS 2,465,319 Whinfield Mar. 22, 1949 2,681,360 Vodonik June 15, 1954 2,739,957 Billica Mar. 27, 1956 2,921,051 Am'borski et a1. Jan. 12, 1960 

1. UN THE PROCESS OF MANUFACTURE OF FIBER- AND FILMFORMING HIGHLY POLYMERIC POLYMETHYLENE TEREPHALATES WHEREIN A DIALKYL TEREPHTHLATE IS REACTED UNDER ESTER INTERCHANGE CONDITIONS WITH A GYLCOL OF THE SERIES 